﻿package Hmin.utils
{
	import flash.utils.ByteArray;

	public class Base64
	{
		private static const BASE64_CHARS:String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

		public static const version:String = "1.0.0";

		/**
		 * 	编码
		 */ 
		public static function encode(data:String):String
		{
			// Convert string to ByteArray    
			var bytes:ByteArray = new ByteArray();
			bytes.writeUTFBytes(data);

			// Return encoded ByteArray    
			return encodeByteArray(bytes);
		}
		
		public static function encodeByteArray(data:ByteArray):String
		{
			// Initialise output    
			var output:String = "";

			// Create data and output buffers    
			var dataBuffer:Array;
			var outputBuffer:Array = new Array(4);

			// Rewind ByteArray    
			data.position = 0;

			// while there are still bytes to be processed    
			while (data.bytesAvailable > 0)
			{
				// Create new data buffer and populate next 3 bytes from data    
				dataBuffer = new Array();
				for (var i:uint = 0; i < 3 && data.bytesAvailable > 0; i++)
				{
					dataBuffer[i] = data.readUnsignedByte();
				}

				// Convert to data buffer Base64 character positions and     
				// store in output buffer    
				outputBuffer[0] = (dataBuffer[0] & 0xfc) >> 2;
				outputBuffer[1] = ((dataBuffer[0] & 0x03) << 4) | ((dataBuffer[1]) >> 4);
				outputBuffer[2] = ((dataBuffer[1] & 0x0f) << 2) | ((dataBuffer[2]) >> 6);
				outputBuffer[3] = dataBuffer[2] & 0x3f;

				// If data buffer was short (i.e not 3 characters) then set    
				// end character indexes in data buffer to index of '=' symbol.    
				// This is necessary because Base64 data is always a multiple of    
				// 4 bytes and is basses with '=' symbols.    
				for (var j:uint = dataBuffer.length; j < 3; j++)
				{
					outputBuffer[j + 1] = 64;
				}

				// Loop through output buffer and add Base64 characters to     
				// encoded data string for each character.    
				for (var k:uint = 0; k < outputBuffer.length; k++)
				{
					output +=  BASE64_CHARS.charAt(outputBuffer[k]);
				}
			}

			// Return encoded data    
			return output;
		}
		
		/**
		 * 解码
		 */
		public static function decode(data:String):String
		{
			// Decode data to ByteArray    
			var bytes:ByteArray = decodeToByteArray(data);

			// Convert to string and return    
			return bytes.readUTFBytes(bytes.length);
		}

		public static function decodeToByteArray(data:String):ByteArray
		{
			// Initialise output ByteArray for decoded data    
			var output:ByteArray = new ByteArray();

			// Create data and output buffers    
			var dataBuffer:Array = new Array(4);
			var outputBuffer:Array = new Array(3);

			// While there are data bytes left to be processed    
			for (var i:uint = 0; i < data.length; i += 4)
			{
				// Populate data buffer with position of Base64 characters for    
				// next 4 bytes from encoded data    
				for (var j:uint = 0; j < 4 && i + j < data.length; j++)
				{
					dataBuffer[j] = BASE64_CHARS.indexOf(data.charAt(i + j));
				}

				// Decode data buffer back into bytes    
				outputBuffer[0] = (dataBuffer[0] << 2) + ((dataBuffer[1] & 0x30) >> 4);
				outputBuffer[1] = ((dataBuffer[1] & 0x0f) << 4) + ((dataBuffer[2] & 0x3c) >> 2);
				outputBuffer[2] = ((dataBuffer[2] & 0x03) << 6) + dataBuffer[3];

				// Add all non-padded bytes in output buffer to decoded data    
				for (var k:uint = 0; k < outputBuffer.length; k++)
				{
					if (dataBuffer[k + 1] == 64)
					{
						break;
					}
					output.writeByte(outputBuffer[k]);
				}
			}

			// Rewind decoded data ByteArray    
			output.position = 0;

			// Return decoded data    
			return output;
		}

		public function Base64()
		{
			throw new Error("Base64 class is static container only");
		}
	}
}